Description. Based on holotype (163.0 mm SL) and 16 paratypes 45.5–192.0 mm SL with notes on variation among smaller specimens. Measurements and counts are summarized in Table 1. Sexes appear to be isomorphic.

Bar 3 extends between the 10 th and 13 th dorsal­fin spines, and runs parallel to bar 2, fading ventrally at H 6 –H 7. Bars 1–3 are generally bisected dorso­ventrally by a lighter column about 1 scale wide, giving the appearance of being two narrow bars in some specimens; this feature may be lost on poorly preserved specimens. A diffuse, blackish medial spot coincides with bar 3, extending rostro­caudally between scales 11–12 and 14–15 of E 3 and dorso­ventrally between E 3 and E 1, such that the upper lateral line traverses the uppermost row of scales of the spot. Bar 4 extends between the bases of dorsal­fin spines 13–14 to 16–18, descends vertically and fades at H 4 –H 5. Bar 5 extends between the first soft ray and ray 4–5 of dorsal fin, it descends vertically and disappears at H 3 –H 4; in other specimens the bar is located between the last dorsal­fin spine and ray 3. Bar 6 extends from the base of the 6–7 (4–5 in some specimens) dorsal­fin rays and extends to the base of the caudal fin; bar is restricted to dorsal portion of caudal peduncle, above lower lateral line, and is longer horizontally than vertically ( Fig. 2
View Figure
b).

Live colors ( Fig. 4
View Figure
). Background color greenish gray, breeding specimens more metallic gray. Head without markings except for iridescent blue on the upper lip, continued as a stripe extending to the corner of the preopercule, and a slight marking of the same color on the ventral edge of orbit. A variable number of iridescent blue spots on the preopercule apparently limited to breeding specimens. Six yellow stripes extend between the base of dorsal and H 4–5; in adult, breeding specimens, dorsalmost stripes appear as brownish­orange vermiculations and spots. Ventrum distinctly white; breeding adults with bright orange or red chest. Dorsal and anal fins reddish with faint iridescent blue horizontal banding that turns brighter during breeding; caudal brownish red with iridescent blue spots and bands in no clear pattern; pelvic reddish orange with iridescent blue banding, first ray white or very light blue. An aquarium photograph in Weidner (2000: 148, Fig. 1
View Figure
) of an unidentified Geophagus from Venezuela is undoubtedly of a mature adult of G. abalios.

Distribution and habitat. ( Fig. 9
View Figure
) Geophagus abalios is commonly found in black or clear water rivers in the llanos, and is known from the Apure, Cinaruco­Capanaparo, and Aguaro­Guariquito drainages. Its current northern­most collection locality is “Las Majaguas” dam in the Río Cojedes, where it was probably introduced by recommendation of the Venezuelan ichthyologist A. Fernández­Yépez. According to his account (Fernández­Yépez and Anton, 1966), Geophagus species were not naturally present in the reservoir, and he recommended the introduction of " Geophagus surinamensis " along with some other species, presumably for sport fishing purposes. G. abalios reaches the Andean piedmont to the west, and is the only Geophagus found in clear to white water seasonal lagoons along the main­stem of the Orinoco to the east ( Rodríguez and Lewis Jr. 1990; 1994). The species appears restricted to the Caura drainage on the Guyana Shield, but it extends into the tributaries of the middle and upper Orinoco, including the Ventuari, Mavaca, and along the Río Casiquiare, nearly to the headwaters of the Río Negro.

Etymology. From the Greek a, not or without and balios, spotted. In reference to the lack of preopercular markings. To be regarded as an adjective in masculine form.